Java 为什么我的图标处理代码会抛出 NullPointerException？

Why does my icon handling code throw a NullPointerException?

提问by Johanna

I have added an image for my button,but when I run that frame this exception will be thrown .why?please help me.

我为我的按钮添加了一个图像，但是当我运行该框架时，将抛出此异常。为什么？请帮助我。

init:

deps-jar:
compile-single:
run-single:
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
        at javax.swing.ImageIcon.<init>(ImageIcon.java:138)
        at ClientGUI.IdAndPasswordFrame.initComponents(IdAndPasswordFrame.java:91)
        at ClientGUI.IdAndPasswordFrame.<init>(IdAndPasswordFrame.java:22)
        at ClientGUI.IdAndPasswordFrame.run(IdAndPasswordFrame.java:200)
        at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:597)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:273)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:183)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:173)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:168)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:160)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:121)
BUILD SUCCESSFUL (total time: 1 second)

line 138:

第 138 行：

public ImageIcon (URL location) {
    this(location, location.toExternalForm());
}

line91:

第 91 行：

 jButton1.setIcon(new javax.swing.ImageIcon(getClass().getResource("/Images/yahoo_1.gif"))); // NOI18N

I use this poor checking (Peter Lang recommended)which is:System.out.println(getClass().getResource("/Images/yahoo_1.gif")); and it returns null,why? please help me.

我使用这种糟糕的检查（Peter Lang 推荐），它是：System.out.println(getClass().getResource("/Images/yahoo_1.gif")); 它返回null，为什么？请帮我。

采纳答案by Peter Lang

This means, that getClass().getResource("/Images/yahoo_1.gif")returns null.

这意味着，getClass().getResource("/Images/yahoo_1.gif")返回null.

JavaDocstates that this happens if

JavaDoc指出，如果

the resource could not be found or the invoker doesn't have adequate privileges to get the resource.

找不到资源或调用者没有足够的权限来获取资源。

1. Check if getResourcereally returns null:
   System.out.println(getClass().getResource("/Images/yahoo_1.gif"));

2. Make sure that your path is correct and that it is in your classpath.

1. 检查是否getResource真的返回null：
   System.out.println(getClass().getResource("/Images/yahoo_1.gif"));

2. 确保您的路径正确并且在您的类路径中。

EDIT:

编辑：

I just tried it with NetBeans. I created the following structure

我刚刚用 NetBeans 试过了。我创建了以下结构

Source Packages
  Images
    yahoo_1.gif

and your code worked fine. Is this your structure?

并且您的代码运行良好。这是你的结构吗？

Try to right-click on your application and select Clean and Build.

尝试右键单击您的应用程序并选择Clean and Build。

回答by rsp

It looks like getClass().getResource("/Images/yahoo_1.gif")returns nulli.e. the .gif cannot be found on your classpath. (Images versus images maybe?)

它看起来像getClass().getResource("/Images/yahoo_1.gif")返回，null即在您的类路径中找不到 .gif。（图像与图像可能？）

回答by Paolo

The URL being passed in is null from this line:

从这一行传入的 URL 为空：

getClass().getResource("/Images/yahoo_1.gif")

From the JDK documentation:

来自 JDK 文档：

[getResource(..) returns] A URL object for reading the resource, or null if the resource could not be found or the invoker doesn't have adequate privileges to get the resource

[getResource(..) 返回] 用于读取资源的 URL 对象，如果找不到资源或调用者没有足够的权限来获取资源，则返回 null

Maybe you meant ("Images/yahoo_1.gif") - i.e. relative path not absolute?

也许你的意思是 ("Images/yahoo_1.gif") - 即相对路径不是绝对的？

回答by Ioana Marginean

In order to fix this, the images need to be copied in the bindirectory - not in srcdirectory.

为了解决这个问题，需要将图像复制到bin目录中 - 而不是src目录中。

Otherwise you will get null all the time on getClass().getResource("image.png"). The path is not nulland you can set it as the above - only if you copy the images that you need inside the binary directory, where .class files for your project are located.

否则，您将始终在getClass().getResource("image.png")上获得 null 。路径不为空，您可以将其设置为上述内容 - 仅当您将所需的图像复制到二进制目录中时，您的项目的 .class 文件位于该目录中。

This fixed the problem. Let me know if I helped in this.

这解决了问题。如果我在这方面有所帮助，请告诉我。

Ioana

约阿纳

回答by 0_o

I had the same problem. What worked for me was:

我有同样的问题。对我有用的是：

1. Look into the jar file or in the bin folder(the one with .class files) and see the path of image.
2. List item

1. 查看 jar 文件或 bin 文件夹（带有 .class 文件的文件夹）并查看图像的路径。
2. 项目清单

回答by sudheer

private class HandlerClass implements ActionListener{
        public void actionperformed(ActionEvent event){
            JOptionPane.showMessageDialog(null, String.format("%s", event.getActionCommand()));
        }

}